The present invention relates to an improved burner nozzle assembly for a pulverized coal burner, and more particularly to a nozzle assembly that promotes fuel rich combustion and reduces the formation of nitrogen oxide emissions.
Many burner configurations have been designed for burning pulverized coal. A problem confronted by such designs is to reduce the production of oxides of nitrogen (NOx) in the combustion process.
U.S. Pat. Nos. 4,479,442 and 4,457,241 disclose a dual air zone, controlled combustion venturi, pulverized coal burner assembly used with front or opposed fired utility boilers to provide low NOx combustion. U.S. Pat. No. 4,517,904 discloses a tertiary staged venturi burner system for reducing NOx emissions from turbo furnace type steam generators. Although the burner assemblies disclosed in these patents have achieved success in providing pulverized coal combustion with low levels of NOx, it would be desirable to provide an improved nozzle assembly for use in these and other burner systems that provides even greater NOx reduction.
A principal object of the present invention is to provide an improved pulverized coal burner nozzle assembly. Other objects are to provide a pulverized coal burner nozzle assembly that promotes fuel rich combustion and reduces the formation of nitrogen oxides; and to provide a pulverized coal burner nozzle assembly that provides an improvement over known burner assemblies.
In brief, in accordance with the invention there is provided a nozzle assembly for use in a pulverized coal burner of the type wherein the nozzle assembly discharges into a surrounding stream of axially flowing air. The nozzle assembly includes an elongated tubular nozzle body having a central longitudinal axis and axially spaced inlet and outlet ends. A coal/air supply introduces a flowing mass of pulverized coal and primary air into the inlet end of the nozzle body for axial flow through the nozzle body to the outlet end. A venturi in the nozzle body between the inlet and outlet ends concentrates the flow of pulverized coal and primary air at the center of the nozzle tube and creates a fuel rich central region,. The venturi includes an upstream converging wall section and a restricted venturi throat. A spreader in the nozzle body between the venturi throat and the outlet end includes a plurality of swirl vanes inclined relative to the axis for imparting a swirling motion to the flow of pulverized coal and primary air. A flow stabilizer mounted at the outlet end of the nozzle body includes a first portion extending radially outward from the nozzle body into the surrounding air stream for deflecting the air stream away from the axis. The stabilizer includes a second portion extending radially inward from the nozzle body into the swirling flow of pulverized coal and primary air.